1. Field of the Invention
This invention relates to training devices and, more particularly, to devices for teaching navigational skills.
2. Description of the Prior Art
For centuries man has navigated by the stars and the sun. However, with the increase in the speed of modern vehicles and with the great expansion of modern travel, more accurate methods of navigation have been required. One of the newer navigational systems is the Omega system which is a long-range hyperbolic navigation system that transmits interrupted continuous wave signals from which phase differences are extracted.
Omega is a radio navigation system employing very low frequency electromagnetic signals which will provide relatively accurate positional information to navigational users on a world-wide basis. This system somewhat resembles other radio navigational systems such as Loran and Decca but differs in a number of important ways. Omega operates at a much lower frequency than does Loran and its position fixing technique utilizes phase differences rather than time differences.
The complete Omega system will consist of eight transmitting stations distributed more or less uniformly over the globe. The primary navigational signal is transmitted at a frequency of 10.2 kHz and a power level of 10 kW. The transmissions from each station are synchronized (to a common reference), unmodulated continuous wave signals which are time-shared within a ten-second interval. Outside a 1,000 km radius (near field) zone, each transmitter radiates a stable signal pattern which is repeated in a radial direction at approximately 30 km segments from the station. These repeated segments, or wave lengths, thus provide a measure of great circle distances and contain a complete cycle of phase which is measured in radians or degrees. The cumulative phase is the total intervening phase between a transmitter and an observation point and hence is approximately proportional to the corresponding great circle distance. In practice, the reference oscillator of an Omega receiver will not ordinarily provide the timing of the time sequenced transmission burst and hence only the fractional portion of the range in wave length units is known. The remaining distance which corresponds to an integral number of wave lengths must be determined by external means. In order that a user's receiver be simple and inexpensive, the system is customarily used in a hyperbolic mode. In this mode, signals from a pair of transmitters are compared to an internal oscillator not time synchronized to the transmitter and a phase difference is measured. The locus of geographic positions which gives rise to the same phase difference with respect to two transmitters is a closed curve on the earth's surface. Clearly, two such curves, referred to as lines of position, obtained from three or four transmitters will establish a position fix. Since the calculation of these lines of position is somewhat involved, charts have been prepared for large areas of the world. Three charts show lines of position latices corresponding to several transmitter pairs and are plotted in sufficient detail such that accurate interpolation can be made.
Simulators have been used as training devices in many situations, but they have a special place in dangerous or potentially dangerous situations. A simulator which is to be used for training is constructed to simulate the operation of a device in real time. That is, the simulator must produce the same effects in the same time that the actual device being simulated does. Thus, simulators have been invented to teach students how to use and operate various types of equipment without undergoing the dangers that are inherent in the equipments' actual operation. For instance, it is a great deal safer to learn how to navigate an aircraft on the ground than to get lost in the air in an acutal aircraft.